You can learn how to load/unload a magazine fed handgun with less than 30 seconds of instruction. Ditto for a revolver. As for "practice", the guy was shooting people at close range. That doesn't require any practice. There is no marksmanship involved. Point and shoot. If you can point a flashlight, you can shoot a target at close range without ever peering down the sights.
I'm betting the guy purchased a bunch of magazines for each pistol and filled all of them before he headed out the door. Swapping a magazine just requires pushing the release to drop the empty, inserting a full mag and releasing the slide.
Ok - another question. Why would he file off (or try to) the serial numbers on the weapon? If he was going to kill himself? That part didn’t make sense - because they are saying he bought the 9 mm at the Roanoke Gun shop and I saw the interview with the gun shop owner....so he didn’t get a gun off the street. Why try to get rid of the serial number?